The present invention relates generally to emergency vent valves and more specifically to emergency vent valve and accelerated application sensor valve of a brake control valve.
A pneumatic brake control valve generally includes a service portion and an emergency portion mounted to a pipe bracket as shown in FIG. 1. The emergency portion 20 is shown as the emergency portion of a DB60, known as DB20 available from New York Air Brake Corporation and is described in U.S. Pat. No. 4,586,756.
The DB - 20 and DB -20L emergency portions currently use an accetrated application sensor valve which is either open or closed, but is otherwise independent to the emergency piston position and pilot pressure (i.e. Brake pipe reduction). This type of feature is an open-loop control system since it is either fully operating or closed. The drawback to this type of system is that in some reductions, the sensor valve may become self propagating. This occurs when relatively short lengths of brake pipe are attached to the emergency portion 20.
The function of the accelerated application is to propagate a brake pipe (BP) reduction signal throughout the train for improved braking application time. This is currently accomplished by the emergency piston moving upward in response to a drop in brake pipe pressure a pre-established distance to open the accelerated application sensor valve. This sensor valve allows quick action volume (QA) pressure to mix with brake pipe in a mixing chamber, and then is exhausted to the atmosphere by way of the accelerated application or pulsating valve. When sufficient brake pipe and quick action volume have been exhausted, the emergency piston stabilizes, closing the sensor valve, and hence arrest accelerated application activity.
However, as the brake pipe to quick action volume ratios decrease for the respective valve designs, the ability of the brake pipe pressure to stabilize the emergency piston becomes more difficult. As mentioned before, the sensor valve is both opened and feeding QA pressure to the mixing chamber, or it is closed stopping the accelerated application activity. As the sensor valve remains open, a constant volume of air is fed to the mixing chamber via a fixed orifice of the sensor valve.
This constant volume of air will continue the accelerated application activity until one of two events occur: 1) the QA pressure reduces to the point were when equalized in the mixing chamber, the pressure is unable to overcome the spring force of the pulsating valve; or 2) the sensor valve closes due to piston stability, stopping the flow of QA pressure to the mixing chamber. If this does not transpire, a further reduction in brake pipe pressure occurs, causing more piston instability, and continuing the cycle.
To eliminate the problem of a self propagating accelerated application, the introduction of a closed-loop control system is necessary. The present design of the emergency vent valve and the accelerated action sensor valve provides a closed-loop control of the accelerated application and stabilization of the emergency piston.
A brake control valve includes a volume and an emergency vent valve connected to an interface of a pipe bracket. The emergency vent valve includes a vent valve for selectively connecting a first brake pipe port to a vent port and a vent piston for controlling the vent valve. An emergency piston includes a first side connected to the volume port and a second side connected to a second brake pipe port A discharge valve is connect to the emergency piston and selectively interconnects the second side of the vent piston, the vent port and the volume port as a function of the displacement of the emergency piston. An accelerated application valve selectively connects the volume port and the second brake pipe port to the vent port in response to pressure from the volume port. An accelerated application sensor valve connected to the emergency piston and selectively connecting the volume port to the accelerated application valve as a function of the displacement of the emergency piston.
In a first embodiment, the discharge valve operates as and replaces the accelerated application sensor valve so as to also selectively connect the volume to the accelerated application valve. In which case, the discharge valve's connection of the vent port and the accelerated application valve to the second side of the vent piston and the volume port is a variable orifice whose opening varies as a function of the displacement of the emergency piston. In a second embodiment, the accelerated application sensor valve has a variable orifice. This may be the separate sensor valve or the combined valve of the first embodiment In a third embodiment, the discharge valve's connection of the vent port to the second side of the vent piston and the volume port is a variable orifice whose opening varies as a function of the displacement of the emergency piston. This discharge valve may be used alone or with the separate sensor valve of the second embodiment.
The variable orifice of the valves may include a valve seat and a tapered valve member connected to the emergency piston.
The discharge valve disconnects the volume port and the second side of the vent piston from the vent port for a brake release position of the emergency piston; connects the volume port and the second side of the vent piston to the vent port for a brake apply position of the emergency piston; and disconnects the volume port from the second side of the vent piston and the vent port and connects the second side of the vent piston to the vent port for an emergency position of the emergency piston.
In the first embodiment, the discharge valve disconnects the volume port from the accelerated application valve for the brake release position of the emergency piston, and connects the volume port to the accelerated application valve for the brake apply position of the emergency piston.
In the second embodiment, the accelerated application sensor valve disconnects the volume port from the accelerated application valve for the brake release position of the emergency piston, and connects the volume port to the accelerated application valve for the brake apply position of the emergency piston.
The discharge valve and the accelerated application sensor valve may be poppet valves in-line with the emergency piston. In the second and third embodiments, the discharge valve may be connected to the emergency piston by a lost motion mechanism such that the accelerated application sensor valve opens before the discharge valve opens.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.